In the manufacture of large scale and very large scale integrated circuits, including semiconductor memories such as high density dynamic random access memories (DRAMs), it is frequently desirable to deposit insulating layers directly on the surface of a semiconductor substrate or wafer being processed so as to form high quality inorganic dielectric layers which may be utilized to form storage capacitors. These integrated circuit type storage capacitors are useful and are required in large numbers, for example, as an AC coupled component for the bit lines and word lines in dynamic random access memory integrated circuits.
As is well known, the capacitance of a dielectric layer or strip is proportional to the dielectric constant, .epsilon., of the layer material times the capacitor plate area, A, divided by the thickness, d, of the dielectric layer. Thus, in the formation of high capacitance storage devices used in the construction of high density integrated circuits where the above capacitance plate area or "A" dimension is very limited, it becomes desirable to use a very thin dielectric capacitor layer with a small "d" dimension of a high dielectric constant material in order to maximize the .epsilon..multidot.A/d quotient.
In the fabrication of these dielectric capacitor layers on the surfaces of silicon substrates, silicon nitride, Si.sub.3 N.sub.4, has been frequently used as the capacitor dielectric material, and this inorganic dielectric material has a relatively high dielectric constant .epsilon. which is approximately twice that of silicon dioxide, SiO.sub.2. Therefore, it is clearly desirable in the manufacture of certain types of integrated circuits to form a single thin layer of only silicon nitride directly on the surface of a silicon substrate and which is then operative to function as the storage node of an integrated circuit capacitor element, such as a storage capacitor of a DRAM memory cell.
However, it has not been heretofore possible to form only Si.sub.3 N.sub.4 on the silicon surface using conventional prior art silicon processing techniques. The reason is that these conventional silicon processing techniques could not be carried out in such a manner as to prevent the formation of a thin native silicon dioxide layer directly on the exposed silicon surface before one could commence depositing the desirable higher dielectric constant silicon nitride layer thereon to form the capacitor dielectric. Thus, the presence of this undesirable native silicon dioxide, SiO.sub.2 layer will simultaneously decrease the value of the dielectric constant .epsilon., increase the value of the total dielectric layer thickness "d" and have the net resulting effect of decreasing the .epsilon..multidot.A/d capacitance quotient value and thus charge storage capability of the integrated circuit capacitor being fabricated.
The only known prior art attempt to solve the above native oxide problem and prior effort toward preventing the formation of this native thermal oxide on the treated silicon surface is to pump and flush oxidizing gases and other residual elements out of conventional low pressure chemical vapor deposition (LPCVD) nitride furnaces using conventional vacuum pumping techniques and flushing with standard inert carrier gases. However, due to the nature, size and mode of operation of these LPCVD nitride furnaces, these attempts have failed to solve the above problem of forming a thin native oxide layer on the silicon surface prior to the initiation of a silicon nitride deposition thereon. That is, these LPCVD nitride furnaces are normally operated so that there is always some oxygen and moisture residue therein.
When the reactant gases are pumped into one end of the LPCVD nitride furnace and the silicon wafers are introduced into the other end thereof in preparation for Si.sub.3 N.sub.4 deposition process, it becomes virtually impossible to prevent the formation of this thin native SiO.sub.2 layer on the silicon wafers being treated. This thin SiO.sub.2 native oxide layer is formed as a result of the fact that the LPCVD nitride furnace is operated at an elevated temperature on the order of about 800.degree. C. or greater in the presence of some oxygen and moisture residue in the main reaction chamber of the LPCVD system.